When you go to an interview you expect to meet and be asked a common series of questions. What if you end up being the one leading the discussion? Asking all the important questions?
That sounds like an unusual interview, but it doesn't necessarily mean it was bad. Sometimes the best interviews just feel like a conversation. The interviewer may just want to get to know you and how you think, and assess whether you could lead a conversation. Either way, if the interviewer does suck, there's not much you can do except show that you're thoughtful, capable, and excited about the opportunity. Which it sounds like you did.